Defect and Diffusion Forum Vol. 344

Abstract: Corrosion rate, corrosion potential and susceptibility to pitting corrosion of a metal are measured using cyclic polarization Direct Current (DC) electrochemical technique. The aim of the present research is to investigate the pit nucleation resistance of polished, ground and passivated surfaces of 316 stainless steels in Ringers solution. The electrochemical cyclic polarization results showed that polished surface gave better pitting resistance as compared to ground surface. It was also observed that passivation treatment gave better pitting resistance to both polished and ground surface of 316 stainless steels in Ringers solution.

Abstract: The present research aims to study the effect of various combination of salt and metal modifiers (SrCl₂, KCl and NaCl salts with NaF including Sb & Sr ) on the locally developed A356 Al-Si alloy. A series of different heats with these modifiers were prepared using a pit type furnace. Casting of the molten metal was carried out using sand casting technique and fluxes at various stages followed by degassing. Sr modifier was used as Al-Sr master alloy, while Sb metal was used in high purity form. However salt modifiers were thoroughly dried before plunging at the bottom of the crucible containing the molten metal. It was observed that the samples containing Sr as modifier showed the best results in terms of microstructure & tensile properties as compared to Sb modifier. A combination of SrCl₂, KCl with NaF showed almost the similar and well modified microstructure with better tensile properties as compared to the samples containing NaCl with NaF salt modifier.

Abstract: NiAl is one kind of high-temperature alloys with broad potential applications in aerospace industry. Its mechanical properties are believed to be largely related to the dislocation behavior and impurity-dislocation interaction. In the paper we report first principles study of the alloying effect of Zr in the [10(010) edge dislocation core of NiAl. The binding energy of doping system decreases 3.77 eV when a Zr atom substituted for an Al, only decreases 1.06 eV with substitution for a Ni atom. The result of the binding energy shows that a Zr atom prefers to occupy an Al site in the dislocation core of NiAl. The analyses of the charge distribution, the interatomic energy and the partial density of states suggest that Zr will greatly enhance the interaction between Zr atom and neighboring host atoms, as well as that between host atoms. These results show that the alloying element Zr induced pinning effect on the edge dislocation motion is predicted, and could be helpful for understanding microscopic mechanisms of alloying-induce hardening in NiAl alloy.

Abstract: The present study aims to develop A356 Al-Si alloy using high purity aluminium and various master alloy in gas fired pit furnace. Three different ratio of salt modifier (1:1, 1:2 & 1:3) was used to prepare the casting. Sand casting and permanent mould casting techniques were used to prepare the alloys. Optical microscope and universal tensile testing machine were used for the metallurgical evaluation of the prepared alloy. It was observed that the addition of modifier improved the mechanical properties and microstructure of the alloy. It was also observed that modifying agent NaF with CaCl₂ in 1:1 ratio has shown the best results in terms of microstructure and the mechanical properties.

Abstract: Structural characteristics and thermal behavior of the conventionally solidified Al₈₀Cu₁₄Fe₆, was investigated by X-ray diffraction, optical microscopy, and differential thermal analysis techniques. It was found that the formation of quasi crystalline phase occurs after annealing for relatively low temperature (500°C) during a short time.

Abstract: Effects of sprue base size and design on flow pattern during aluminum gravity casting have been investigated by employing different sprue base sizes and using computational fluid dynamics (CFD). Calculations was carried out using SUTCAST simulation software based on solving Navier-Stokes equation and tracing the free surface using SOLA-VOF algorithm. Flow pattern was analyzed with focusing on streamlines and velocity distribution in sprue base, runner and in-gate. Increasing well size was produced a vortex flow at the bottom of sprue base which increased the urface velocity of liquid metal in runner. Using a rather big sprue well could eliminate vena contracta, but in-gate velocity was observed independent from well size. It assumes that in-gate velocity may be more influenced by other casting considerations. Using a curved sprue base could remove vortex flow at the bottom of sprue while keeping a nearly full contact between liquid metal and runner wall.

Abstract: The performance of organic coatings on steel substrates is strongly affected by substrate cleanliness and anchor patterns. During present research work, Surface pre-treatments were applied to remove contaminants from steel surfaces. Electrochemical Impedance Spectroscopy (EIS) was used to characterize such surfaces in terms of electrochemical parameters to find out the extent of activeness of prepared surfaces, and electrochemical processes are modeled into corresponding electrical equivalent circuits (EECs). Surface roughness parameters were evaluated to find out the extent of mechanical interlocking between prepared surface and the coating to be applied over it. The optimum surface preparation technique prior to application of organic coating was characterized.

Abstract: Hydrogen diffusion and trapping in AISI 316L stainless steel and pure nickel are studied with thermal desorption spectroscopy method. Specific features of hydrogen uptake and desorption for a multi-component alloy in comparison with that for pure metal and the effects of hydrogen concentration profile after electrochemical charging on the hydrogen desorption are discussed. It is shown that hydrogen diffusion and trapping in multi-component alloy are caused by the specific atomic distribution of hydrogen in the crystal lattice of alloy.

Abstract: By the methods of Auger-spectroscopy and mass-spectrometry of secondary ions, small-angle electron diffraction, X-ray and resistometry analyses the solid-state reactions in the Ti(5 nm)/ Ni(24 nm)/Si₍₀₀₁₎ thin film system at annealing in running nitrogen in the temperature interval of 723 – 1273 К are investigated. Regularities of phase transformations, consistency of solid-state reactions, layer-by-layer redistribution of components during annealing, features of surface morphology during formation of inclusions of silicide phases are established.

Abstract: The isotropic g factor and hyperfine structure constant for Ir⁴⁺ in CdO are theoretically studied from the perturbation formulas of these parameters for an octahedral 5d⁵ cluster based on the cluster approach. The calculated results show good agreement with the experimental data. The ligand orbital contributions should be taken into account due to significant covalency of the system with high impurity valence state even in the oxide.